Optical enantiomorphs of homoserine and homocystine

Abstract

Chloroacetyl- dl-homoserine lactone was synthesized. After opening the ring at pH 8, and treating with hog kidney acylase I, dl-homoserine ([ α] D = −8.8 ° in water and +18.3 ° in 2 N HCl) was obtained in 72% yield. From the mother liquor, chloroacetyl- d-homoserine was separated, yielding on HCl hydrolysis the lactone of d-homoserine · HCl ([ α] D = +26.7 ° in water). Refluxing of the lactone at pH 8 resulted in d-homoserine in 60% yield ([ α] D = +8.6 ° in water and −18.2 ° in 2 N HCl). A sample of the lactone of l-homoserine · HCl prepared by refluxing l-homoserine with HCl yielded [ α] D = −27.0 ° in water. N-Acetyl- S-benzyl- dl-homocysteine was subjected at pH 7.5 to the action of acylase I, yielding S-benzyl- l-homocysteine in 85% yield ([ α] D = +27.2 ° in 2 N HCl) and N-acetyl- S-benzyl- d-homocysteine. The latter compound after refluxing with HCl followed by neutralization yielded S-benzyl- d-homocysteine in 65% yield with [ α] D = −27.3 °. From the S-benzyl derivatives, l- and d-homocystine were prepared by du Vigneaud's procedure, with [ α] D respectively of +77.5 ° and −77.5 °. The l-enantiomorphs of homoserine and S-benzylhomocysteine are readily oxidized by Crotolus adamanteus venom l-amino acid oxidase, and the corresponding d-enantiomorphs by hog kidney d-amino acid oxidase. By means of these preparations it was determined that the l-and d-enantiomorphs of the two amino acids were more than 99.9% optically pure.